1. Field of the Invention
The present invention relates to a rotary ring spinning device provided with a ring motor, particularly to a rotary ring spinning device provided with a ring motor in combination with a drive control device.
2. Description of the Related Art
Several rotary ring spinning devices have been developed for a ring spinning frame, ring twisting frame, and roving twister etc., as a yarn winding and twisting device, and some are now utilized in practice. Typical of these devices is the spinning device disclosed in Japanese Unexamined Patent application, Showa 63(1988)-223249.
With regard to the drive system of these rotary ring spinning devices, a positive means for driving the rotary ring, such as utilizing compressed air or a friction pulley, or a negative means for driving the rotary ring, such as utilizing a torque obtained from the frictional pressure generated by a traveller when running around a flange of each ring, are known.
A rotary ring spinning device provided with a ring motor, whereby the rotary ring is electrically driven, is also known [Japanese Unexamined Patent Publication Showa 61 (1986)- 152835]. According to the disclosure of this patent publication, because the rotary ring is driven by an outer-rotor system, the rotary ring must be provided with a larger space than other known rotary rings, as the additional space is needed in particular for the windings of electric wiring forming an armature, of a rotor and for an iron core thereof. Therefore, a larger space must be provided when using the above-mentioned rotary ring, compared with the other types of rotary ring mentioned above. Also, the following problem arises in that the spindle pitch must be enlarged when adopting such a rotary ring spinning device having a larger size due to the drive system. This problem is very serious because the number of spindles in a unit floor space must be reduced, and thus the production capacity of a ring spinning machine utilizing this type of rotary ring spinning device having a larger size is lowered, compared to the use of the other type of rotary ring spinning device.
Since the running speed of the spindle of the other known rotary ring spinning devices is usually maintained within a range of 20,000 to 22,000 r.p.m., and in particular case, a test of the running speed at 30,000 r.p.m. was successfully carried out, if in the rotary ring spinning device provided with an outer-rotor system driving more mentioned above, to maintain the production capacity at the same level as obtained with the above-mentioned known rotary ring spinning device, it is necessary to rotate such a rotary ring spinning device at a higher speed such as between 40,000 and 60,000 r.p.m., because such a rotary ring spinning system needs more installation space than the other known rotary ring spinning device, and therefore, the number of spindles to a spinning frame is reduced in comparison with the above-mentioned other known rotary ring spinning devices. Such a high speed driving of the spindles, however, is not practical, because of problems arising from the machine construction, vibration of the spinning frame, power consumption costs, maintenance of yarn quality, and operation control, etc. On the other hand, as a means for eliminating problems due to possible . variations of the yarn tension over a wide range, in the conventional spinning practice certain methods for adjusting the spinning conditions, such as lowering the spindle speed by 10-20% to the speed at which the spindle is driven during formation of a medium size package, during formation of a yarn package from the start to 20-30% of the full yarn package, and during formation of a yarn package from 80-90% of the full yarn package, or a method using a cushion start system for starting the spinning operation, are applied because, during the above-mentioned periods of forming a full sized yarn package, there is a tendency toward an occurrence of frequent yarn breaks. Accordingly, the yarn producing capacity during such a period of adjusting the spindle speed is naturally reduced.
It is further known that, in the case of a negative rotary ring spinning device utilizing a thrust bearing or a pneumatic supporting system, the turning torque of the rotary ring, which corresponds to a relationship between the weight of the rotary ring and the friction pressure of the traveller at the rotary ring, is varied in accordance with variations of the yarn tension, variations due to changes of the stretch length, and instant positioning of the ring rail, which is related to the formation of a part of a yarn package and further, a lifting motion of the ring rail, which involves a building motion, variations of the running speed of a traveller during the formation of each chase of a yarn package, and other factors. Nevertheless, even under such conditions, since the weight of the rotary ring is constant, when the upright component of the spinning tension, which pulls the rotary ring upwards along the spindle shaft, exceeds the weight of the rotary ring, the rotary ring rotates at a higher speed. Therefore, if a braking device is not utilized, the speed of rotation of the rotary ring is gradually increased, and accordingly, the working condition of the bearing portion becomes the same as a condition of a pneumatic bearing, and the driving speed of the rotary ring rapidly reaches the rotary speed of the traveller.
Once the rotation speed of the rotary ring is synchronized with the running speed of the traveller, even if the running speed of the traveller is changed during the formation of the yarn package in each chase, the rotation speed of the rotary ring is maintained at an almost constant value due to the inertia of the rotary ring. Therefore, the difference in the traveller running speed when the yarn is wound around a cop at the uppermost position of each chase, and when the yarn is wound around the cop at the lowermost position of an identical chase, reaches remarkable values [running speed of the traveller in the former condition becomes half of the running speed of the traveller in the latter condition]. Accordingly, there is a strong possibility that the rotation speed of the rotary ring can overrun the running speed of the traveller, and thus the spinning yarn tension is remarkably varied between positive values and negative values.
Due to the occurrence of this abnormal condition, the yarn passing over the traveller is severely abraded, and thus the yarn quality is lowered. When spinning a yarn of artificial fibers, problems such as the creation of neps due to abrasion, cutting of fibers forming the yarn (creation of neppy yarn), creation of melted portions of the yarn or yellowing of portions of the yarn due to the friction-heat, and frequent yarn breakages, occur.
To solve the above problems, in the operation of the conventional rotary ring spinning devices, the rotation speed of the rotary ring must be maintained at a value lower than the running speed of the traveller, and therefore, it is necessary to create a friction-resistance between the rotary ring and the traveller. But if the yarn tension, which includes a tension based upon the friction-resistance, becomes greater than the inherent strength of the yarn, the spinning yarn is forcibly broken. Therefore, when utilizing the conventional rotary ring, the rotation speed of which cannot be positively controlled, the rotation speed of the spindle is always restricted to a speed 20% to 30% lower than the upper rotation limit of the spindle of the conventional spinning device. In other words, in the case of utilizing the rotary ring spinning devices, a higher speed operation of the spinning frame than that of the conventional spinning device has not been achieved. On the other hand, as a negative rotary ring spinning device which is provided with a function of preventing a synchronous rotation of the rotary ring with the running speed of the traveller, Japanese Unexamined Patent Publication Showa 58 (1983)-156037 discloses a rotary ring spinning device provided with a friction braking device. In addition to the above-mentioned rotary ring spinning device, the applicant has developed a rotary ring spinning device provided with a magnetic braking device actuated by an eddy electric current [Japanese Patent Application Showa 63 (1988)-137931]. Although these rotary ring spinning devices are useful in practice, the former device has a problem of abrasion of the brake shoe, and in the latter device, an exchange of the rotary ring provided with the magnetic brake having a different magnetic force suitable for carrying out the spinning operation for a yarn concerned is required when the type of spinning yarn is changed.